For any research project, you want to use a variety in types of sources as well as points of view. Some assignments will have certain requirements for the sources, in terms of genre of source (academic, popular), format (blog, print) and publication dates. To research a question in depth, the answer to the question of “how many and what type of sources do I need” is all of them. You need a variety of sources, both in type and point of view, in order to fully (or even partially) explore a research question.